Negative electrode active material, method for producing the negative electrode active material, and lithium ion secondary battery using the negative electrode active material

Abstract

Disclosed is a negative electrode active material which has a high capacity and good cyclability. The negative electrode active material comprises nanosize carbon particles and nanosize tin dioxide particles that are supported in a high-dispersion state on the nanosize carbon particles. The negative electrode active material has a high discharge capacity because of the reversible progress of a conversion reaction of tin dioxide (SnO 2 +4Li + +4 e − →2Li 2 O+Sn) therein. In a charge-discharge cycle test within a voltage range of 0 to 2 V vs. an Li/Li + electrode, the negative electrode active material shows a discharge capacity retention rate of about 90% even after 500 charge-discharge cycles at the rate 1 C, which indicates excellent cyclability. Therefore, the negative electrode active material can be suitably used in a lithium ion secondary battery and a hybrid capacitor.

1 - 21 . (canceled) 
     
     
         22 . A negative electrode active material capable of reversibly occluding and releasing lithium comprising:
 a conductive carbon powder; and   nanosize tin oxide particles supported on the carbon powder, wherein 30% by mass or more of primary particles of tin oxide is not aggregated.   
     
     
         23 . The negative electrode active material according to  claim 22 , wherein the tin oxide particles have an average diameter of 1 to 10 nm. 
     
     
         24 . The negative electrode active material according to  claim 22 , wherein the carbon powder is composed of nanosize particles. 
     
     
         25 . The negative electrode active material according to  claim 24 , wherein the nanosize carbon particles are composed of Ketjen Black. 
     
     
         26 . The negative electrode active material according to  claim 24 , wherein a mass ratio of the carbon particles and the tin oxide particles is within a range of 20:80 to 40:60. 
     
     
         27 . A negative electrode active material capable of reversibly occluding and releasing lithium comprising:
 a nanosize conductive carbon powder; and   a tin oxide powder,   
       wherein 30% by mass or more of primary particulates of the carbon powder and the tin oxide powder is not aggregated. 
     
     
         28 . The negative electrode active material according to  claim 27 , wherein the tin oxide powder is composed of nanosize particles. 
     
     
         29 . The negative electrode active material according to  claim 28 , wherein the tin oxide particles have an average diameter of 1 to 10 nm. 
     
     
         30 . The negative electrode active material according to  claim 29 , wherein the carbon powder has inner vacancies and the tin oxide particles substantially exist in the inner vacancies. 
     
     
         31 . The negative electrode active material according to  claim 30 , wherein the carbon powder is composed of Ketjen Black. 
     
     
         32 . The negative electrode active material according to  claim 28 , wherein the carbon powder is composed of particles having an average diameter of 10 to 50 nm. 
     
     
         33 . The negative electrode active material according to  claim 28 , wherein the carbon powder has the surface area of 1,000 m 2  or more per gram. 
     
     
         34 . The negative electrode active material according to  claim 28 , wherein the carbon powder has oxygen of 5.0 mmol or more per gram. 
     
     
         35 . A method for producing a negative electrode active material according to  claim 22  comprising:
 a step of introducing a reaction liquid prepared by adding a conductive carbon powder to a solution in which a tin salt is dissolved into a rotatable reactor; and 
 a step of rotating the reactor so as to induce a hydrolysis reaction and a polycondensation reaction of the tin salt while adding shear stress and centrifugal force on the reaction liquid and concurrently support a reaction product obtained on the carbon powder. 
 
     
     
         36 . A method for producing a negative electrode active material according to  claim 28  comprising:
 a step of introducing a reaction liquid prepared by adding a nanosize conductive carbon powder to a solution in which a tin salt is dissolved into a rotatable reactor; and 
 a step of rotating the reactor so as to induce a hydrolysis reaction and a polycondensation reaction of the tin salt while adding shear stress and centrifugal force on the reaction liquid and concurrently support a reaction product obtained on the carbon powder. 
 
     
     
         37 . The method for producing a negative electrode active material according to  claim 36 , wherein Ketjen Black is used as the carbon powder. 
     
     
         38 . The method for producing a negative electrode active material according to  claim 37 , wherein the reactor comprises concentric cylinders of an outer cylinder and an inner cylinder, the inner cylinder having through-holes provided on the side surface thereof, the outer cylinder having a sheathing at the aperture thereof, so that, by centrifugal force produced by rotation of the inner cylinder, the reaction liquid in the inner cylinder is moved to an inner wall surface of the outer cylinder through the through-holes, a thin film containing the tin salt is formed on the inner wall surface of the outer cylinder, and the hydrolysis reaction and the polycondensation reaction of the tin salt are expedited when the shear stress and the centrifugal force are added to the thin film. 
     
     
         39 . A lithium ion secondary battery comprising:
 a negative electrode comprising a negative electrode active material according to  claim 22 ;   a positive electrode comprising a positive electrode active material capable of reversibly occluding and releasing lithium; and   a separator retaining a nonaqueous electrolytic solution placed between the negative electrode and the positive electrode.   
     
     
         40 . A lithium ion secondary battery comprising:
 a negative electrode comprising a negative electrode active material according to  claim 27 ;   a positive electrode comprising a positive electrode active material capable of reversibly occluding and releasing lithium; and   a separator retaining a nonaqueous electrolytic solution placed between the negative electrode and the positive electrode.   
     
     
         41 . A lithium ion secondary battery comprising:
 a negative electrode comprising a negative electrode active material according to  claim 31 ;   a positive electrode comprising a positive electrode active material capable of reversibly occluding and releasing lithium; and   a separator retaining a nonaqueous electrolytic solution placed between the negative electrode and the positive electrode.